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2010 Honda Civic Unstable Low Pressure Needle
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The_G
New User
Jul 16, 2020, 4:22 PM
Post #1 of 7
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2010 Honda Civic Unstable Low Pressure Needle
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Make & Model: Honda Civic
Year: 2010
Engine: 1.8L V4
Of all the material I have gone through to diagnose A/C issues, I have yet to find the same case that I’m running into, as most guides just diagnose with just a given PSI for high or low side. Many guides don’t even acknowledge the effects of ambient temperature.
Main Points:
Not enough cooling (here in Vegas in July it’s already hard to get)
AC Compressor Engages
Low-Side needle was very unstable, while High-Side was stable
System was ~38 on low side, and 200 on high side upon first measurements (in ~105 F), engine brought up to temp
Per mechanic friend’s recommendation: Tried charging the system up to 250 on the high side to see if I could get it there, and I did successfully
Low side needle still highly unstable (rapid shaking and also varied what it was centered around between 50-60 psi), while high side varies a but but the needle doesn't shake like the low side.
Friend’s Guess: Probably a leak somewhere in the system and/or a clogged expansion valve.
Waiting to look at the car again to check the UV dye I put into the system and look for leaks.
Thoughts?
Note: I do have access to a vacuum pump, but I haven't picked it up yet. I was not able to perform the test to see if the vehicle holds vacuum yet.
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Hammer Time
Ultimate Carjunky
/ Moderator
Jul 16, 2020, 4:58 PM
Post #2 of 7
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Re: 2010 Honda Civic Unstable Low Pressure Needle
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OK, some very important basics.
You CANNOT charge a system by pressures. The very first step is to evacuate and recharge the system with the specified weight of refrigerant. Only then can the pressures be used to gain information about how the system is operating. The pressures mean nothing if you don't know exactly how much refrigerant is in the system.
Once that is done we can look at the pressures and give you a very good idea what is going on.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jul 16, 2020, 5:02 PM
Post #3 of 7
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Re: 2010 Honda Civic Unstable Low Pressure Needle
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Pressures don't tell you if it's full just if within the perimeters that it should be at all of a given temp, idle speed and ability of it overall.
LV hot - understood. This I thought holds almost 24oz but ALWAYS use any stickers under hood as the capacity of the system. Vacuum pumps are rentable as well as gauges thru many auto parts outlets but TMK not in CA think you should ask around.
A or B for choices. Get a scale or if close 134a is sold in 12oz cans of pure product no games, sealers or other additive you need to (legally) have it recoverd (what's left inside) and charge it to exact # of ounces. Only then when know charge weight was put into a vacuum can you begin to know if system works at all then if not up to par pressures really help diagnose what is wrong.
# 1 reason is low charge from a leak but don't freak yet it's 10 years old, doesn't hold all that much and it works hard where you are as bad as anywhere! Worse - lack of shade and surface you may be on would cook an egg no problem.
If you wish to DIY it do just that then need to know for real input temp of air thru grille, output temp of a center vent on re-circulate with a raised idle.
Sorry - sounds and is a lot yes or no depending on you and not messing it up watch all info while charging or stop.
Top post (locked here) may help you is a nasty read like this is it's an involved algorithym of temps/pressures and speed of compressor by known RPM.
Don't be so scared to have just that done it's engaging so isn't empty is 1/2 the battle now just see if it works with known charge and how long before it looses it. Then find the leak is it's own art sometimes Vegas should be easier if you can stand it to work right where you have to did a lot over phone to there with retired friends over the years!
Tom
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The_G
New User
Jul 26, 2020, 2:18 PM
Post #4 of 7
(942 views)
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Re: 2010 Honda Civic Unstable Low Pressure Needle
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Had some delays to get at the car. Thank you for your input! I'm taking this into consideration
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The_G
New User
Jul 26, 2020, 2:19 PM
Post #5 of 7
(940 views)
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Re: 2010 Honda Civic Unstable Low Pressure Needle
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Had some delays to get at the car. Thank you for your feedback! I really wasn't aware I couldn't diagnose from the pressures alone. Big thanks for the information
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Hammer Time
Ultimate Carjunky
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Jul 26, 2020, 2:22 PM
Post #6 of 7
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Re: 2010 Honda Civic Unstable Low Pressure Needle
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I didn't say that you couldn't diagnose by pressures. I said that you couldn't CHARGE by pressures.
The pressures give you vital information but only after it has the precise amount of charge in the system.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jul 26, 2020, 3:55 PM
Post #7 of 7
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Re: 2010 Honda Civic Unstable Low Pressure Needle
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Disregard if I'm just confusing but think of those pressures and also think of engine oil how much you put in going only by oil pressure vs you have a dipstick. A/C does NOT so just like an engine missing a dipstick or knowing it's correct in all aspects dump it and put in the known # of quarts for that case.
That's the raw basic idea: Once known then all other info, symptoms, noises pressures mean something A/C pressures are sooooo temp dependent by minutes with a running engine just can't tell you the weight of the charge will screw up if off and not by much % wise vs the oil analogy.
When in doubt stop and understand it or seek help it's a dynamic thing live in front of you can't just be faked and work up to damage so beware,
Tom
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